They also allow reviewing commits individually, which is very frustrating to do without dedicated support (unless you devolve back to mailing list patch stacks).
It's a big improvement (assuming they've done it right).
I'm not a huge fan, since stacked PRs mean the underlying issues don't get addressed (reviews clearly taking too long, too much content in there), but it seems they want something that works for their customers, right now, as they work in real life.
I guess this is why you're getting downvoted. Commits can be edited.
If I had to guess a reason they were downvoted (and I didn't downvote, to be clear), it's probably because people see stacked diffs as specifically solving "reviews clearly taking too long, too much content in there", and so it feels contradictory. Then again, as I said, I didn't downvote!